The present invention relates to an engine arrangement having an engine comprising an EGR system and a charge air cooler.
It is known from the state of the art that an engine arrangement having an engine, preferably for a vehicle such as a truck, bus, lorry, car, boat or the like, comprises an EGR system. In internal combustion engines, exhaust gas recirculation (EGR) represents a nitrogen oxide (NOx) emission reduction technique used in petrol/gasoline and diesel engines. NOx primarily forms when mixture of nitrogen and oxygen is subjected to high temperatures. EGR works by recirculating an engine exhaust gas portion back to the engine cylinders. In a gasoline engine, this inert exhaust gas displaces the amount of combustible matter in the cylinder. In a diesel engine, the exhaust gas replaces some of the excess oxygen in the pre-combustion mixture. Since NOx formation progresses much faster at high temperatures, EGR reduces the amount of NOx generated as a result of combustion. Replacing air with EGR lowers the lambda value whereby EGR lowers the combustion temperature and reduces the concentration of O2.
An EGR cooler is a heat exchanger installed in the EGR circuit. The EGR system recirculates exhaust as back to the engine in order to reduce NOx emissions. The cooler simply cools the exhaust gas prior to reintroduction of the gas into the engine. By cooling the gas, the combustion temperature is decreased, whereby NOx is formed at higher temperatures. During this cooling process, EGR gas may become excessive, for example during engine start or during a cold start period, deteriorating the combustion efficiency in each cylinder and in the exhaust gas components. Hence, the EGR system having the EGR cooler is arranged in this instance so as to cause the EGR gas to flow in an EGR bypass provided by bypassing a passage of the EGR cooler. For switching this EGR cooler during use and during non-use, a passage switching valve is frequently used to change a flow of exhaust gas from one direction to another direction or to two directions or a flow of exhaust gas from two directions to one direction, or from one direction to another direction.
It is also known in the state of the art to use a turbocharger or turbo compressor in an internal combustion engine, which is a gas compressor to enhance induction of air in an engine cylinder or which is a form of a supercharger. The turbocharger increases the density of air entering the engine to produce more power. A turbocharger has the compressor being powered by a turbine which is driven by the engine's own exhaust gas. Compressing air in the turbocharger increases the air temperature, which may cause a number of problems. Excessive charge air temperatures can lead to detonation, which is highly detrimental to engines. When a turbocharger is installed on an engine, it is common practice to fit the engine with an intercooler system (also known as a charge air cooler system, or CAC system), being a type of heat exchanger which releases heat energy in the charger to ambient air. For a compression ignition engine having at least one turbocharger and an intake air cooler, operation of the engine at or around idle is difficult to optimize for various reasons. Firstly, due to the aspect that low ambient temperature air flows into the engine through the intake charge air cooler under low ambient temperatures, the air entering the intake manifold may be over-cooled and, when an exhaust gas recirculation (EGR) system is utilized, may cause excessive carbon deposits on the EGR valve and intake sensors. Secondly, low intake air temperatures at idle engine conditions may result in undesirable white smoke and odors in the exhaust gas of compression ignition engines due to incomplete combustion of the fuel. Therefore, CAC bypass valves are known in spark ignition engines e.g. in aeroplane motors for preventing motor failure due to ice formation in the CAC at high altitudes and in gasoline internal combustion engines e.g. for reducing white smoke during cold start.
In order to reduce emissions, a selective catalytic reduction catalyst (SCR catalyst) is widely used, converting NOx with the aid of a catalyst into diatomic nitrogen, N2, water, H2O. A gaseous reductant, typically anhydrous ammonia, aqueous ammonia or urea, is added to a flue or exhaust gas flow and is absorbed onto a catalyst. A SCR catalyst works more efficiently with warmer exhaust gas. Starting with diesel engines manufactured on or after Jan. 1, 2010, engines are required to meet lower NOx standards. A majority of heavy-duty engine (Class 7-8 trucks) manufactures utilize such SCR catalysts to efficiently reduce NOx emissions to meet upcoming EPA standards, which are the emission standards of the United States. The EU has introduced Euro 4 being effective since Jan. 1, 2008, Euro 5 being effective since Jan. 1, 2010 and will introduce Euro 6 taking effect on Jan. 1, 2014. Asian countries, such as China, India and Japan, pursue similar regulations.
From U.S. Pat. No. 7,257,950 B2 an engine arrangement is known comprising a CAC system and an EGR system, wherein the CAC system comprises a CAC bypass. The CAC bypass enters the EGR system at a cold side of the engine.
In order to meet the above-mentioned emission standards, it is desirable to provide an engine arrangement, wherein the exhaust gas temperature can be controlled in an optimal way under various engine and environmental conditions, especially at low engine load and/or low engine or low external air temperature, such that a SCR catalyst is enabled to work efficiently.
It is also desirable to provide an engine arrangement with improved emission values based on various existing engine arrangements with a high packing density, such that a voluminous modification, additional installations and reconstruction can be avoided. In this way, existing engine arrangements can be modified to meet improved emission standards with little effort.
Aspects of the invention are directed to solving problems noted above.
An engine arrangement is proposed according to an aspect of the invention, comprising an engine, a charge air cooler connected to an engine inlet side of the engine, an air bypass for bypassing the charge air cooler, and comprising an EGR system connected between an engine outlet side and an engine inlet side of the engine via one or more EGR lines. The air bypass enters the EGR system at an air-bypass port of an EGR line for mixing air with exhaust gas at the engine outlet side of the EGR system and/or upstream of an EGR cooler. In order to arrange the CAC air bypass on the engine outlet side of the EGR system, which is the high temperature side of the engine, charged air mixes with exhaust gas at the hot side of the EGR system, e.g. between a downstream side of a high temperature EGR cooler (HT EGR cooler) and an upstream side of a low temperature EGR cooler (LT EGR cooler). In order to transform an existing engine arrangement into an inventive arrangement, an additional CAC air bypass line and an air-bypass port can be installed connecting the CAC system and the EGR system at a high temperature side of the engine, which is a slight modification of an existing engine arrangement. A predetermined thickness of the air bypass line, a flow orifice or a binary or proportional throttle can control the amount of charged air flowing through the air bypass into the EGR system. Thus, an optimized air/exhaust gas mixture is provided at low ambient temperature and/or low engine load such that an increased exhaust gas temperature can be provided for enabling a SCR catalyst to work more efficiently. Existing components of an engine arrangement can be used such that modification effort is minimal. Early mixing of charged air and exhaust gas decreases the temperature in the EGR system so that certain components of the EGR system, such as thermal insulation and cooler dimensions, can be reduced providing additional constructional space. In an engine arrangement having a dual-stage turbo compressor, the air bypass should be arranged downstream of the second compressor.
According to an advantageous embodiment of the invention, a control device may be provided for controlling an engine inlet temperature T_in of an air/exhaust gas mixture by controlling a ratio of cooled/uncooled air and/or cooled/uncooled exhaust gas in the air/exhaust gas mixture. The ratio between air and EGR can remain the same and can depend on engine parameters like combustion condition, speed, load etc. The inlet temperature T_in can be controlled by cooling or not cooling the charge air using a CAC bypass valve or throttle. Furthermore the inlet temperature T_in can be controlled by cooling or not cooling the EGR using an EGR cooler bypass valve or throttle. Both types of controlling amount of cooled/uncooled charged air and cooled/uncooled exhaust gas can be used in a combined way and can also be used independently from another. The control device can control the above mentioned ratio such that an optimized exhaust gas temperature can be provided for the SCR catalyst. Typically, hot exhaust gas has a hot temperature of 650° C. to 700° C., and cold exhaust gas (low load or cold engine) has a temperature of 100° C. to 350° C. Turbocharged air has a typical temperature of 50° C. to 280° C. The engine inlet temperature is crucial for exhaust gas emission and for the lubricating system of the engine. If T_in is too high, an engine oil film may deteriorate. The control device can control the ratio such that a mixture of cooled/uncooled exhaust gas and cooled/uncooled charged air enters the engine inlet side at a predefined temperature and ratio independent of engine load and temperature, for instance with T_in>60° and T_in<125° C., optimally T_in in a range between 100° C. to 120° C., such that an SCR catalyst is enabled to work efficiently. The control device can be a controller system or the like comprising means for measuring, or evaluating an actual engine inlet temperature in a direct manner (temperature sensor) or indirect manner (based on driving conditions using a map considering accelerator pedal angle, clutch status or the like). The control device can be connected to one or more binary or proportional throttles or valves located in the EGR system line, CAC system line and/or air bypass line in order to control an amount of air or gas flowing through the air or gas line. The control device can be connected to an EGR cooler and/or CAC system to control cooling temperature and can control a gas flow through an EGR cooler bypass and/or air flow through a CAC air bypass such that an air/exhaust gas mixture can enter the engine at a predefined temperature T_in.
According to a second aspect of the invention, an engine arrangement, particularly as mentioned above, comprises an engine, a charge air cooler connected via an airline to an engine inlet side of the engine, an air bypass for bypassing the charge air cooler, and an EGR system connected between an engine outlet side and an engine inlet side of the engine via one or more EGR lines. The control device is provided for controlling an engine inlet temperature T_in of an air/exhaust gas mixture by controlling a ratio of cooled/uncooled air and/or cooled/uncooled exhaust gas. The control device can control the flow of cooled air through the CAC system, the flow of cooled exhaust gas through the EGR system and/or the flow of uncooled air through the air bypass and optionally the flow of cooled EGR through an EGR cooler and/or uncooled EGR through an EGR cooler bypass such that the exhaust gas temperature can be provided high enough for the SCR catalyst but low enough under a critical temperature, thus avoiding damage to the engine. The control device can be arranged as described above.
According to an advantageous embodiment of the aforementioned engine arrangement, the control device can control the engine inlet temperature T_in of the air/exhaust gas mixture by mixing uncooled air from the air bypass or cooled air from a charge air cooler with exhaust gas from the EGR system at the engine outlet side of the EGR system. The control device can control at least a throttle or valve opening or closing the air bypass passage such that a ratio of uncooled air flowing through the air bypass and cooled air flowing through the charge air cooler can be adjusted. A first throttle disposed in the airline and a second throttle disposed in the air bypass line can control the amount of air and the ratio of cooled/uncooled air for mixing with the EGR. The air bypass line can enter the EGR system at an EGR line with an EGR cooler or can enter the EGR system at an EGR cooler bypass line.
According to an advantageous embodiment, the control device can control the engine inlet temperature T_in of the air/exhaust gas mixture mixing charged air with uncooled exhaust gas from an EGR bypass or with cooled exhaust gas from an EGR cooler. The control device can control at least a throttle or valve opening or closing an EGR cooler bypass passage such that a ratio of uncooled exhaust gas flowing through the EGR bypass and cooled exhaust gas flowing through the EGR cooler can be adjusted. A first throttle disposed in the EGR bypass and a second throttle disposed in the EGR cooler line can control the amount of EGR and the ratio of cooled/uncooled EGR for mixing with the charged air.
The controlling device can control the passage through the air bypass line and the EGR bypass line for controlling the ratio of cooled/uncooled EGR mixed with cooled/uncooled air independently and can also combine the control of both ratios for optimizing the exhaust gas temperature such that an SCR catalyst can work efficiently at all load and temperature conditions.
According to an advantageous embodiment, a throttle can be arranged in the airline. The throttle can be a binary throttle or valve for opening or closing the airline or can be a proportional throttle or valve such that an amount of air flowing through the airline can be controlled. Closing the throttle separates the CAC system from the EGR system on the hot side of the engine. Opening the throttle enables mixing of air and exhaust gas within the EGR line between hot side and cold side of the engine. If an EGR cooler bypass line exists it can also be favourable to arrange a throttle in the EGR bypass.
According to an advantageous embodiment, a throttle can be arranged in the airline and the air bypass. The airline connects a turbocharger with the CAC system. Opening or closing the airline throttle actives/deactivates cooling of the charged air. Preferably at low load of the engine, the airline throttle should be closed and the air bypass throttle should be opened. At high load, the air bypass throttle should be closed. If an EGR cooler bypass line exists it can also be favourable to arrange a throttle in the EGR bypass and in the EGR line.
According to an advantageous embodiment, the engine inlet temperature T_in of the air/exhaust gas mixture can be determined between a minimum temperature T_scr and a maximum temperature T_max. The maximum temperature T_max can be chosen so as to prevent damage to the engine, especially at low load or at low ambient temperatures, and can be chosen to be preferably T_max<=125° C. The minimum temperature T_scr can be chosen to guarantee low emissions of the engine, preferably such that a SCR catalyst is enabled to work efficiently and can be set T_scr>=60° C. Values of T_scr and T_max may vary depending on the current engine status and environmental and driving conditions. The minimum and maximum temperature T_scr, T_max can be taken from a map.
According to an advantageous embodiment, the engine outlet side and the engine inlet side can be connected via a direct EGR line free of an EGR cooler, and the air bypass can enter the EGR system via the direct EGR line. Additionally, the direct EGR line can be an EGR bypass for bypassing one or more EGR coolers, e.g. a HT and/or a LT EGR cooler. As a consequence, the direct EGR line can be an EGR cooler bypass line for bypassing one or more EGR coolers in a low temperature state of the exhaust gas. Exhaust gas can flow either partly or selectively through the direct EGR line or through an EGR line comprising at least one EGR cooler. Charged air can flow through the direct EGR line independent of the flowing direction of the exhaust gas.
According to an advantageous embodiment, the air bypass can enter the EGR system between a first EGR cooler and a second EGR cooler. The first EGR cooler can be a HT EGR cooler and the second EGR cooler can be a LT EGR cooler. The air bypass enters the EGR system downstream of the HT EGR cooler and upstream of the LT EGR cooler and the air is mixed with pre-cooled exhaust gas. As a consequence, the dimensions of the LT EGR cooler and the insulation thickness of the EGR line downstream of the HT EGR cooler can be reduced, since temperature of the mixed air/exhaust gas can be further decreased.
According to an advantageous embodiment, an EGR line segment can be arranged downstream of the air bypass port in the EGR line and can be adapted as a mixing chamber. The air bypass enters the EGR system either upstream of an EGR cooler or can be connected to a direct EGR line. The EGR line downstream of the air bypass port leads to the cold side of the engine and can be adapted for adequately mixing charged air and exhaust gas. Thus, the EGR line segment functionally acts as a mixing chamber and can be adapted in form, width and internal configuration to provide thorough mixing of air and exhaust gas during the flow between air bypass entry point and inlet into the engine's cylinder.
According to an advantageous embodiment, the charge air cooler can be an air-cooled device or can be a coolant-cooled device. Furthermore, it may be possible to use a hybrid-cooled device having an air-cooled and a coolant-cooled part. Cooling performance of a coolant-cooled device can be controlled in limited ranges such that efficient control of the inlet temperature of the exhaust gas/air mixture by controlling the cooling behaviour of the CAC system is possible. A hybrid-cooled device can be used for scaling the cooling performance dependant on the engine's temperature status.
According to another aspect of the invention, a vehicle is proposed comprising an engine arrangement according to any of the above-mentioned embodiments. The vehicle's engine comprises a CAC system and an EGR system, wherein the temperature of an exhaust gas/charged air mixture at an engine's inlet on the cold side of the engine can be controlled such that the vehicle emissions can be reduced preferably in a low load situation or at a low ambient temperature. A conventional vehicle can be converted into an embodiment of the invention by installation of an air bypass between an airline upstream of the CAC system and an EGR line at the hot side of the engine. Additionally, a control device comprising means for sensing an exhaust gas/air mixture inlet temperature and one or more throttles for controlling, gas/air flow in the air bypass, EGR system and/or CAC system, can be provided to meet upcoming emission standards.